Hello, Here is a tutorial's small patch addressing the issue pointed out by Warren Weckesser in https://lists.ginac.de/archives/list/ginac-list@ginac.de/thread/IPVLGB2E6ZCA... Best wishes, Vladimir -- Vladimir V. Kisil http://v-v-kisil.scienceontheweb.net Book: Geometry of Mobius Maps https://doi.org/10.1142/p835 Soft: Geometry of cycles http://moebinv.sourceforge.net/ Jupyter notebooks: https://github.com/vvkisil?tab=repositories